1. Field of the Invention
The present invention relates to a presence system using SIP (Session Initiation Protocol)/SIMPLE (SIP for Instant Messaging and Presence Leveraging Extensions). In particular, it relates to a load balance server and a method for balancing load of presence information (presence state).
2. Description of the Related Art
SIMPLE is a technology developed from SIP to realize an instant message and a presence service, according to (1) “Session Initiation Protocol (SIP)—Specific Event Notification”, RFC3265, (2) “Session Initiation Protocol (SIP) Extension for Event State Publication”, RFC3903 and (3) “A Presence Event Package for the Session Initiation Protocol (SIP)”, RFC3856.
According to the presence service, one user terminal's status (for example, “on-line”, “off-line”, “busy” or “absent”) is push-sent to other user terminal. Not only the user status but also the presence information of efficiency or position in the terminal is sent.
Further, 3GPP (3rd Generation Partnership Project) is standardizing a presence system in IMS (IP Multimedia Domain) using SIP/SIMPLE, according to (4) “Presence service using the IP Multimedia (IM) Core Network (CN) subsystem; Stage 3 (Release 7)”, 3GPP TS 24.141 V7.3.0 (2006-12).
FIG. 1 is a system configuration diagram of presence system in the prior art.
According to FIG. 1, a plurality of user terminals communicates with one presence server 2. A plurality of user terminals has a presentity function and/or a watcher function. “Presentity” means “Presence+Entity”, and shows an ownership of the presence information. “Watcher” means “SUBSCRIBER”, and corresponds to “presentity”.
(S101) Presentity 3 generating presence information sends PUBLISH message to register presence information to presence server 2. Correspondingly, the presence server 2 sends back a 200OK message to the presentity 3. The registration of the presence information is managed in soft-state. Thus, the presence server 2 cancels a registration of the presence information unless a PUBLISH message of re-registration (REFRESH) is received in effective period.
(S102) It is assumed that a user operating watcher 4 wants to subscribe to presence information in presentity 3 had by other users. Then, watcher 4 sends a SUBSCRIBE message for requiring subscription of the presence information in presentity 3 to presence server 2. Correspondingly, the presence server 2 sends back a 200OK message to watcher 4.
The presence information is identified by a combination of PRS-URI (PReSence-Uniform Resource Identifier, identifier for the presence information of the presentity) and Event (event name, event package). The subscription of the presence information is also managed in soft-state. Thus, presence server 2 cancels the subscription of the presence information unless a SUBSCRIBE message is received in effective period. In the case of re-subscription, a SUBSCRIBE message including the dialogue same as the subscription of the first time must be sent. That is to say, id parameters of header fields of To tag, From tag, Call-ID and Event must be the same.
(S103) After receiving the SUBSCRIBE message, the presence server 2 sends back an NOTIFY message including the presence information to watcher 4. Correspondingly, the watcher 4 sends back a 200OK message to presence server 2.
Also, there is the case that presentity 3 sends a PUBLISH message for modifying (MODIFY) the presence information to presence server 2. In this case, an NOTIFY message including updated presence information is sent to all watchers 4 subscribing the presence information.
According to the previously described presence system, when presence information is increased, a load of the presence server and the network is increased, too. Specifically, when there are a great number of the transmission of PUBLISH messages including the presence information, the number of the transmission of NOTIFY messages is also increased. In particular, when there are a great number of the transmission of SUBSCRIBE messages for one presence information, the number of the transmission of NOTIFY messages for one PUBLISH message is also increased.The number of NOTIFY messages=number of SUBSCRIBE messages*number of PUBLISH messages
When the number of user terminals is increased, expansibility in the presence system is limited.
Conventionally, there are layer 7 switches controlling transmission route based on the frame header of SIP message to realize load balance. When this is applied to a presence system, for example, every PRS-URI and Event, the PUBLISH message including the presence information can be sent to the presence server by path control.
However, the watcher must send a SUBSCRIBE message to the presence server that registers the presence information by the PUBLISH message because other presence servers do not store the presence information. Thus, a lot of SUBSCRIBE messages are sent intensively to the presence server that stores a specific presence information. That is to say, there is a problem that the presence server becomes a heavy-loaded.